temperature switch for LCD?

**IceX** · 03-25-2008, 07:43 AM

Hi Guys,

I need to build a temperature switch (very cheap) at lower hardware level that will:

1. Allow me to set the on / off temperatures.
2. I need to set the min temp to turn on the device.
3. I need to set the max temp to switch off the device.

I need to please have someone explain me on how to design this. I have done almost research for 7 days now and did not find anything (expect for someone selling something similar):

The problem is this device is for only heater or cooler, cannot control both at same time and their rated amps are very low...

I am looking for circuit diagrams for such a project. To give more details behind this.

The input voltage = 12V dc rated 1.3amps

I need the switch / relay to close (powering the device) when the device is between the min / max temp and to open (stop power) when the device is below the min or above the max.

I need the exact same 12V dc rated 1.3amps output.

Reason:
This is to turn on the LCD screen, but I can only do this in the min / max ranges. Sometimes the car stands in the sun and it takes about 2 minutes for car to cool down with airflow ect.

This will avoid the LCD from obtaining damage due to being turned on while too hot or too cold.

I have fans and everything hooked up, but only want to switch power to the LCD if this is in the operating temp as indicated by manufacturer of LCD.

Thank you.

I need to know which parts to buy and how they will fit into the circuit diagram, I have pcb board, I have soldering station, I have all the toys, just not the know how.

**nemoid** · 03-25-2008, 08:42 AM

you'd really need two controls to do what you want.

either that, or a simple cpu that you can read the information from the thermometer and a program would act accordingly would do the job.

maybe an arduino board would work.

**insaneramman** · 03-25-2008, 07:47 PM

A home heating and cooling thermostat could be used. I would use a digital. The old ones use liquid mercury (it would need to be level at all times). OR get a cheap therm-meter and hang it in your car.

**pir8radio** · 03-27-2008, 12:48 PM

http://www.alliedelec.com/Images/Pro...ol_9286056.pdf

that is a link to a pdf file, you will need to purchase two one for the low temperature and one for the high. They are mechanical thermal switches. You will need one that opens at low temperature and one that opens at hight temperature. This way if it is cold it will open the circuit until it warms up, and if it is hot it will open the circuit until it cools down. you will still need to switch the power when you turn the key on or what ever.

+12vdc ---------O---------O------------ LCD +in
cold hot sensors